Alberto Sierra, 28, is facing three counts of first-degree murder, sexual battery on an adult and sexual battery on a minor in the deaths of Gladys Machado and her 4- and 6-year-old daughters, Miami-Dade Police said.

According to an arrest affidavit, Sierra, Machado and the girls went to the Mall of the Americas on Nov. 10 where Sierra and Machado got into an argument.

Sierra armed himself with a knife, and Machado sustained injuries as a result of the argument there, the affidavit said. He then drove Machado and her daughters to a home in the 7300 block of Northwest 4th Street, where he locked the girls in one of the bedrooms and forced Machado into the master bedroom, the affidavit said.

Once in the master bedroom, Sierra suffocated Machado with a plastic bag "and subsequently sexually assaulted her," the affidavit said.

Sierra let one of the girls out of the bedroom and suffocated her, the affidavit said. He suffocated the other daughter with a plastic bag while she slept, then sexually assaulted the other daughter, the affidavit said.

The bodies of Machado and her daughters were found last Tuesday in a closet at the home, police said.